Many different types of building or utility materials, such as wallboard insulation, blown-in insulation, acoustical or sound dampening/absorbing materials, etc. exist in the art. These are all designed to provide a specific function within a structure. In addition, the composition of ingredients or components making up these utility materials varies greatly. Although there are many different available compositions making up the many different utility materials, relatively few of these incorporate microparticles, such as naturally occurring cenospheres or synthetically manufactured Extendospheres™, into their makeup.
In addition, many different types of naturally occurring and artificial microparticles exist. Cenospheres are naturally occurring microparticles that are part of the “fly ash” byproduct generated in coal burning plants. Billions of tons of coal are burned annually in many plants worldwide to generate electricity, and as a result, over 100 million tons of coal or fly ash byproduct is produced. Fly ash is the fine powder formed from the mineral matter in coal, consisting of the noncombustible matter in coal plus a small amount of carbon that remains from incomplete combustion. It is called “fly” ash because it is transported from the combustion chamber by exhaust gases. Fly ash is generally light tan in color and consists mostly of different sized glassy spheres, the cenospheres. Properties of fly ash vary significantly with coal composition and plant operating conditions. Only a small percentage of the total amount is used, with the rest being disposed of mainly in landfills. Increasing cost and heightened regulations are making the disposal of fly ash an undesirable option. Although fly ash has found its way into a variety of useful applications in different industries, including the building and construction industries, for one or more reasons its success as a suitable utility or building material has been limited. Two specific classes of fly ash are defined by ASTM C618: Class F and Class C. The class distinction relies principally on differing content of components in the ash. As such, the differing classes can behave chemically different. One major distinction is the amount of lime or calcium oxide typically present. In Class F fly ash, generally less than 10 wt % is present. On the contrary, in Class C fly ash, generally more than 20 wt % lime is present.
In addition, there are several artificially manufactured microparticles used for a variety of purposes. Although such microparticles tend to be more consistent and uniform in their makeup and structure, they also tend to be extremely expensive and cost prohibitive for many applications.
Of particular concern in many building structures is how well noise or sound travels through the partitions or walls of the building structure, whether these are interior or exterior walls. In most cases, it is desirable to keep sound transmission across partitions as minimal as possible. Therefore, the ability for structural partitions or walls to attenuate (e.g., absorb or scatter) sound is an important design consideration. Most building materials, such as insulation, some wallboard products, etc., are designed with some degree of sound attenuation or absorption properties in mind as it is often desirable to minimize, or at least reduce, the amount of sound transmission through a partition. With respect to building structures, building materials such as wallboard, insulation, and certain types of paint, are considered materials that can contribute to enhanced sound attenuation properties, or in other words, a reduction in sound transmission.
Wallboard is a common utility or building material, which comes in many different types, designs, and sizes. Wallboard can be configured to exhibit many different properties or characteristics, such as different sound absorption, heat transfer and/or fire resistance properties. By far, the most common type of wallboard is drywall or gypsum board. Drywall comprises an inner core of gypsum, the semi-hydrous form of calcium sulphate (CaSO4.½ H2O), disposed between two facing membranes, typically paper or fiberglass mats.
The most commonly used drywall is one-half-inch thick but can range from one quarter (6.35 mm) to one inch (25 mm) in thickness. For soundproofing or fire resistance, two layers of drywall are sometimes laid at right angles to one another. Drywall provides a thermal resistance, or R value, of 0.32 for three-eighths-inch board, 0.45 for half inch, 0.56 for five-eighths inch and 0.83 for one-inch board. In addition to increased R-value, thicker drywall has a slightly higher Sound Transmission Class (STC) rating.
STC, part of ASTM International Classification E413 and E90, is a widely used standard for rating how well a building material attenuates airborne sound. The STC number is derived from sound attenuation values tested at sixteen standard frequencies from 125 Hz to 4000 Hz. These transmission-loss values are then plotted on a sound pressure level graph and the resulting curve is compared to a standard reference contour. Acoustical engineers fit these values to the appropriate TL Curve (or Transmission Loss) to determine an STC rating. STC can be thought of as the decibel reduction in noise that a wall or other partition can provide. The dB scale is logarithmic, with the human ear perceiving a 10 dB reduction in sound as roughly halving the volume. Therefore, any reduction in dB is significant. The reduction in dB for the same material depends upon the frequency of the sound transmission. The higher the STC rating, the more effective the barrier is at reducing the transmission of most common sound frequencies.
Conventional interior walls in homes or buildings have opposing sheets of drywall mounted on a stud frame or stud wall. In this arrangement, with the drywall panels having a ½ inch thickness, the interior wall measures an STC of about 33. Adding fiberglass insulation helps, but only increases the STC to 36-39, depending upon the type and quality of insulation, as well as stud and screw spacing. As wallboard is typically comprised of several sheets or panels, the small cracks or gaps between panels, or any other cracks or gaps in the wall structure are referred to as “flanking paths,” and will allow sound to transmit more freely, thus resulting in a lower overall STC rating.
Similarly, the Outdoor-Indoor Transmission Class (OITC) is the widely used standard for indicating the rate of transmission of sound between outdoor and indoor spaces. OITC testing typically considers frequencies down to 80 Hz and is weighted more to lower frequencies.